Hybrid fiber-coax (HFC) networks employ a combination of optical fiber and coaxial cable in the network to provide services, such as video, voice, and high-speed Internet, to users over an existing cable television network. A multi-service operator (MSO) uses the HFC network to deliver the above services to users using cable modem termination systems (CMTSs) located at a head-end or hub and customer premise equipment (CPE) devices located at a user's premises.
Typically, the optical fiber network is terminated at an optical node in the HFC network, which then converts the optical signal into an electrical signal. The electrical signal is sent via radio frequency (RF) over the coaxial cable to the user's premises. RF amplifiers following the node are needed to amplify the signal. A typical network topology may be a “node +6” network topology, where “+6” denotes 6 RF amplifiers following the node. Over time, the penetration of optical fiber closer to the users' premises has occurred (known as “fiber deep”). This limits the need for using radio frequency (RF) amplifiers following an optical node. The fiber deep topology reduces the number of RF amplifiers that are needed after the node, and in some cases, reduces the need all the way to zero, which is referred to a “node +0” fiber deep HFC network. In this case, no RF amplifiers are needed if the fiber penetrates deep enough into the HFC network towards the premises.
Using the fiber deep topology, a single node can only reach around 100 premises. This is often too small a size to be designated as a service group. A service group is a group of customer premise equipment devices that are serviced by a cable modem termination system (CMTS) port or converged cable access platform (CCAP) port. The reasoning as to why more than 100 premises are desired relies on economics and statistics that will not be discussed. Due to the desire to have larger service groups than 100, service group aggregation is used to increase the size of a service group.
One way to perform service group aggregation is to “daisy chain” digital optical return signals for multiple nodes to perform upstream aggregation. This aggregates optical return signals for multiple CPEs connected to multiple nodes into a single signal. While this increases the service group number, the aggregated signal also sums the noise floors that are present. The aggregation of the noise floors results in a reduction of the signal-to-noise ratio (SNR) performance.